The present invention relates to a valve monitoring and control system.
In the machinery control industry by which presses, brakes, or the like are actuated by fluid controlled valves, the determination of the position of the movable valve elements is important since upon initial installation, loss of fluid pressure, during servicing, or during replacement of the valves operation of the machinery controlled thereby can be accurately predicted. Without such a control system, the punch press or similar device controlled by the valve can unexpectedly or inadvertently be operated upon start up or return of fluid pressure resulting in serious injury to operators, maintenance personnel, or others. The problem is particularly serious when fluid type poppet valves including a shiftable poppet element are employed which can be moved to any one of a plurality of positions to control the passage of pressurized fluid through the valve.
Several mechanical methods are known for attempting fail safe operation of such valves typically by providing bias springs to maintain the valves in a predetermined position in the event air pressure is lost. In some cases detents are employed to also provide a similar function. The problem with such prior art is that the fail safe features themselves are subject to wear and failure during the continued operation of the valves.
U.S. Pat. No. 4,046,165 issued Sept. 6, 1977, to Rose, Sr., et al illustrates an improvement over this prior art by which a valve positioning means is attached to the valve housing which does not impede normal operation of the valve and which assures the valve is in a predetermined position when air pressure is lost. Although the invention of the above identified patent represents a significant improvement over the prior art, it is desirable to continuously monitor the condition of actuation of a valve and particularly dual valves used for presses and the like to determine if the actual state of the valve corresponds to the state called for by the control signal to the valve actuating solenoids.